Major developments have taken place in vehicular braking systems in recent years. Among these developments are anti-lock braking systems (ABS) and regenerative braking systems used in electric and hybrid-electric systems. In regenerative braking systems, a vehicle's brake pedal is mechanically decoupled from the downstream braking circuits. Sensors associated with the brake pedal provide electrical signals to an electronic control unit (ECU). These signals are representative of the brake pedal position. Since the brake pedal is mechanically decoupled from the downstream braking circuits, a brake pedal feel simulator is often used to simulate the feel of a conventional braking system by providing pressure feedback to the vehicle operator at the brake pedal. The force of the brake pedal is transferred to the brake pedal feel simulator. Meanwhile, the ECU controls the braking system to apply a braking force consistent with the brake pedal position. An electrical regenerative system and/or a hydraulic system provide the necessary braking force.
In the event of a failure of the hydraulic system or the electrical regenerative system, it will become necessary for the braking system to switch its mode of operation so that the brake pedal is mechanically coupled to the downstream brake circuits. In its changed mode, the force applied to the brake pedal would be transferred to the downstream brake circuits to generate the necessary braking force to halt a vehicle.
Therefore, there is a need to provide an improved braking system that is operable in a conventional mode in which a brake pedal is mechanically decoupled from the downstream braking circuits and a fallback mode in which the brake pedal is mechanically coupled to the downstream braking circuits.